Along with the digitization and increasing precision of electronic devices, digitization is progressing for the processing conventionally performed by analog circuits. For example, speed and precision increases are progressing for optically coupled insulating devices as well. Therefore, high speed and high precision is required also of analog-to-digital converters that digitize analog physical quantities; and various methods have been proposed.
Such methods include delta-sigma analog-to-digital converters using delta-sigma modulation, which are known as analog-to-digital converters having high precision and medium speed. Although it is possible to obtain a highly integrated delta-sigma analog-to-digital converter having low current consumption by using a switched-capacitor integrator, high precision requires a high sampling frequency.
Much research and development has been carried out regarding delta-sigma modulations. For example, there have been proposals to compensate errors due to the finite gain of an operational amplifier and compensate the errors due to the finite gain and offset voltage of an operational amplifier.